1. Field of the Invention
The present invention relates to an optical scanning apparatus and an image forming apparatus including the optical scanning apparatus.
2. Related Art
A known optical scanning apparatus typically includes two optical scanning units such as a polygon mirror, two light sources provided respectively corresponding to each optical scanning unit, and four primary mirrors provided respectively opposite and sandwiching each optical scanning unit to reflect light from each light source that is scanned by each optical scanning unit. The optical scanning units are driven to rotate about a rotation shaft, and the rotation shafts are configured in parallel. An example of this type of optical scanning unit is illustrated in FIG. 1.
FIG. 1 is a sectional view of the above type of conventional light scanning apparatus X1.
As illustrated in FIG. 1, the conventional optical scanning apparatus X1 includes two polygon mirrors PM1, PM2, a light source (not shown) provided at two positions corresponding to each polygon mirror PM, and four primary mirrors M11, M12, M21, M22 provided respectively opposite and sandwiching each polygon mirror PM to reflect light from each light source that is scanned by each polygon mirror PM. L11-1, L11-2 (or L12-1, L12-2, L21-1, L21-2, L22-1, L22-2) are respectively f-theta lenses. FIG. 1 illustrates a configuration of one group formed by two f-theta lenses.
In FIG. 1, reference numeral 1 (1BK, 1M, 1Y, 1C) denotes a photosensitive member. A laser beam (hereinafter referred to as “light”) emitted from each light source is scanned by the rotating polygon mirror PM, passes through the f-theta lenses L11-1, L11-2 (or L12-1, L12-2, L21-1, L21-2, L22-1, L22-2), is reflected by the primary mirror M11 (or M12, M21, M22), and becomes incident upon the photosensitive member 1 to thereby form an electrostatic latent image.
This type of light scanning apparatus X1 allocates one polygon mirror PM with respect to two light sources, and therefore enables a reduction in the number of polygon mirrors. As a result, the light scanning apparatus X1 can reduce manufacturing costs.
However, the light scanning apparatus X1 as illustrated in FIG. 1 is configured by one polygon mirror PM, two primary mirrors M11, M12 (or M21, M22) provided opposite and sandwiching the polygon mirror PM and reflecting light scanned by the polygon mirror PM, and thereby, configures a single light scanning unit PU. The problem arises that the two light scanning units PU, PU as illustrated in the figure are merely have a simple configuration along a plane, and therefore the length K in the direction of orientation of the optical scanning units PU, PU as shown by the arrow Y is increased, and the overall apparatus size is increased.